01 - Preheat oven to 350°F. Grease a 9x13-inch baking dish or a 9-inch round springform pan.
02 - In a medium bowl, combine the chopped pecans, brown sugar, cinnamon, flour, and melted butter. Mix until crumbly and set aside.
03 - In a separate bowl, whisk together the flour, baking powder, baking soda, and salt until evenly distributed.
04 - In a large mixing bowl, beat the softened butter and granulated sugar using an electric mixer until light and fluffy, about 3 minutes.
05 - Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract until fully incorporated.
06 - Alternately add the dry ingredient mixture and sour cream to the butter mixture, starting and ending with the flour. Mix until just combined without overmixing.
07 - Spread half of the cake batter evenly into the prepared pan. Sprinkle half of the cinnamon pecan crunch mixture over the batter.
08 - Spread the remaining batter over the filling layer and top with the remaining cinnamon pecan crunch mixture, pressing gently.
09 - Bake for 40 to 45 minutes, or until a toothpick inserted into the center comes out clean and the top is golden brown.
10 - Allow the cake to cool in the pan for 20 minutes before slicing and serving warm.